Proldn-RNA crossfinking inEscherichia coli30S ribosomal subunits. Identification of a 16S rRNA fragment crosslinked to protein S12 by the use of the chemical crosslinking reagent 1-ethyl-3-dlmethyl-aminopropylcarbodlimide

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Abstract
1-ethyl-3-dimethyl aminopropylcarbodiimide (EDC) was used to crosslink 3OS ribosomal proteins to 16S rRNA within the E.coli 3OS ribosomal subunit. Covalently linked complexes containing 3OS proteins and 16S rRNA, isolated by sedimentation of dissociated crosslinked 3OS subunits through SDS containing sucrose gradients, were digested with RNase T1, and the resulting oligonucleotide-protein complexes were fractionated on SDS containing polyacryla-mide gels. Eluted complexes containing 3OS proteins S9 and S12 linked to oligonucleotides were obtained in pure form. Oligonucle-otide 5′terminal labelling was successful in the case of S12 containing but not of the S9 containing complex and led to identification of the S12 bound oligonucleotide as CAACUCG which is located at positions 1316–1322 in the 16S rRNA sequence. Protein S12 is crosslinked to the terminal G of this heptanucleotide.